1. Field of the Invention
The present invention relates to a technique of enabling redundant communication between nodes in a network, and, more particularly, to a packet communication method and a packet communication device capable of effectively using a communication bandwidth of a backup communication path in 1:1 redundant communication. In the 1:1 redundant communication, nodes are interconnected by a working communication path and the backup communication path. When the working communication path operates under normal conditions, no redundant packets are transmitted via the backup communication path.
2. Description of the Related Art
Currently, multipoint communication and the effective use of a bandwidth, which is achieved by bandwidth priority control, attract attention as techniques for use in a network such as an Ethernet network. The scope of application of these techniques has increased.
With the increase in the scope of application of these techniques, a fast failure recovery technique, that is, a technique for protecting a working communication path is required. For example, there is a known method utilizing the STP (Spanning Tree Protocol) as an Ethernet protection technique. However, since switching is performed in units of seconds in the known method, the known method cannot be used for the network of a common carrier. In order to overcome this difficulty, the ITU (International Telecommunication Union) made the recommendation G.8031 that enables fast switching (on the order of a few tens of milliseconds).
FIGS. 1 and 2 show the configuration of known 1:1 redundant communication corresponding to a configuration described in the ITU recommendation G.8031.
Here, if a communication path in a network is represented using the reference numbers of nodes in the network, a working communication path can be represented by a communication path 101-103-104-105-102. In the following description, this notation is used to represent a communication path. Accordingly, a backup communication path can be represented by a communication path 101-106-107-108-102.
Under normal conditions, that is, when the working communication path 101-103-104-105-102 is operating normally, traffic 200 for network users flows via the working communication path 101-103-104-105-102 as shown in FIG. 1. When a failure occurs in the working communication path 101-103-104-105-102, a communication path through which traffic passes is changed from the working communication path 101-103-104-105-102 to the backup communication path 101-106-107-108-102 using switching nodes 101 and 102, and traffic 201 is caused to flow the backup communication path 101-106-107-108-102 as shown in FIG. 2. Consequently, the working communication path 101-103-104-105-102 is protected. A switching control packet 203 for instructing control of switching between the working and backup communication paths is always transmitted between the switching nodes 101 and 102 via the backup communication path 101-106-107-108-102.
For example, if the network is an Ethernet network, VLAN (Virtual Local Area Network) based protection modes, that is, 1:1 unidirectional and bidirectional protection modes and 1+1 unidirectional and bidirectional protection modes are defined. In a bidirectional switching system, the APS (Automatic Protection Switching) protocol is used. The APS control packet 203 for instructing a bridge (corresponding to the switching node 101 shown in FIG. 1) and a selector (corresponding to the switching node 102 shown in FIG. 1) to perform switching between the working and backup communication paths is fed to the backup communication path 101-106-107-108-102. The bridge and selector form the protection entity defined by the G.8031 recommendation. This APS control packet includes switching control request information (including identification information used to determine whether the working communication path is used) for the bridge and selector and information on the condition of each node. The switching nodes 101 and 102 receive and process this APS control packet, whereby the control of switching between the working and backup communication paths is performed.
Under normal conditions, users' traffic is not fed to the backup communication path 101-106-107-108-102 as shown in FIG. 1. That is, if the traffic 200 passes through the working communication path 101-106-107-108-102, there is no traffic in the backup communication path 101-106-107-108-102 other than the APS control packet 203, which is used to instruct the bridge and selector (switching nodes 101 and 102) defined by the G.8031 recommendation to perform switching control. Thus, the efficiency of the communication bandwidth of the backup communication path 101-106-107-108-102 is low.
The ATM protection recommendation (I.630) that uses the same system as Ethernet and the SDH protection recommendation (G.841) also define transmission and reception of traffic carried by the backup communication path while the working communication path is active in the 1:1 (bidirectional) protection mode, that is, define transmission and reception of extra traffic. However, the transmission and reception of the extra traffic is performed via the bridge and selector in accordance with the existing recommendations, that is, is limited to the transmission and reception of traffic via the switching nodes 101 and 102 shown in FIGS. 1 and 2. Accordingly, for example, it is difficult to perform transmission and reception of traffic in a closed communication path between nodes 106, 107, and 108 without causing the traffic to pass through the switching nodes 101 and 102. This is an impediment to the effective use of the communication bandwidth of the backup communication path.
As a related technique, Japanese Unexamined Patent Application Publication No. 7-95227 discloses a protection method for use in the case of a ring network.